The present invention relates to a method for the exact determination of the speed of a rotating part, in particular the speed of the wheel of a motor vehicle, in which discontinuities present on the circumference of the rotating part are scanned without contact and, upon the detection of a discontinuity, an electric pulse is produced and the number of pulses so produced is counted, the invention relating also to a system for carrying out the method.
Known systems for detecting the speed of motor vehicles utilize a signal which is supplied by a single speed transmitter for the determination of the speed of the vehicle.
For this purpose, incremental disks are provided on the front wheel of the motor vehicle. The speed transmitter, for instance a Hall sensor or an inductive transmitter, is arranged facing a wheel of the vehicle or facing the drive shaft of the wheel, or on the transmission output of the drive shaft, preferably on the left front wheel, and detects the speed of rotation of that wheel.
The speed of rotation of the wheel is calculated from the signal of the speed transmitter by counting the signal flanks during a predetermined period of time. This electric signal, which corresponds to the speed of rotation of the wheel, is fed to a controller which determines the speed of the vehicle from the signal.
Due to manufacturing tolerances on the wheel flanks of the increment transmitters with respect to each other and the occurrence of ovalization of the wheels or rims, there result, with this type of evaluation of the wheel speeds of rotation, peaks in the wheel speeds which lead to inaccuracies and falsify the actual wheel speed. These peaks are normally eliminated by filtering the signal.
If the wheel speeds are filtered excessively by the above-described method, the wheel speed determined in this manner loses dynamism.